Virtual colonoscopy (VC) refers to a method of diagnosis based on computer simulation of standard, minimally invasive endoscopic procedures using patient specific three-dimensional (3D) anatomic data sets. Examples of current endoscopic procedures include bronchoscopy, sinusoscopy, upper gastro-intestinal endoscopy, colonoscopy, cystoscopy, cardioscopy, and urethroscopy. VC visualization of non-invasively obtained patient specific anatomic structures avoids risks, such as perforation, infection, hemorrhage, and so forth, associated with real endoscopy, and provides the endoscopist with important information prior to performing an actual endoscopic examination. Such understanding can minimize procedural difficulties, decrease patient morbidity, enhance training and foster a better understanding of therapeutic results.
In virtual colonoscopy, 3D images are created from two-dimensional (2D) computerized tomography (CT) or magnetic resonance (MR) data, for example, by volume rendering.
These 3D images are created to simulate images coming from an actual endoscope, such as a fiber optic endoscope. This means that a viewpoint of the virtual endoscope has to be chosen inside a lumen of the organ or other human structure, and with a wide angle of view, typically about 100 degrees of arc. This viewpoint has to move along the inside of the lumen, which means that a 3D translation and a 3D rotation have to be applied. Controlling these parameters interactively is a challenge.
A commonly used technique for navigating a viewpoint of a virtual endoscope is to calculate a “flight path” beforehand and automatically move the viewpoint of the virtual colonoscope along this path. However, this technique requires a segmentation and trajectory calculation step that is time-consuming and can fail.
Applicant's prior patent application Ser. No. 10/322,326, filed Dec. 18, 2002, and entitled AUTOMATIC NAVIGATION FOR VIRTUAL ENDOSCOPY and whereof the disclosure is hereby incorporated herein by reference to the extent it is not incompatible with the present invention, discloses a system and method of navigation inside a colon dataset, using the longest view ray to advance. The aforesaid prior patent application shows a system and method for automatic navigation of a viewpoint of an endoscope in virtual colonoscopy is provided. The system determines automatically a direction and orientation of a virtual endoscope. Therefore a user needs to control only one parameter—forward or backward speed and the method allows immediate interactive navigation inside an organ without preprocessing, e.g. segmentation and path generation. The method shown in the said application includes the steps of (a) determining an initial viewpoint of the virtual endoscope, the initial viewpoint having a first center point and a first direction; (b) determining a longest ray from the initial viewpoint to the lumen, the longest ray having a first longest ray direction; (c) determining a second direction between the first direction of the initial viewpoint and the first longest ray direction; (d) turning the viewpoint to the second direction and moving the initial viewpoint a first predetermined distance in a first direction of the initial viewpoint; (e) calculating a second center point of the viewpoint; (f) moving the viewpoint to the second center point; and repeating steps (b) through (f) until the viewpoint reaches an intended target.